Site selective excitation, upconversion and laser operation in Er3+:LiKYF5

The energy level structures of Er3+ ions occupying two, almost identical, low symmetry Y3+ sites in LiKYF5 have been determined using site selective laser excitation and luminescence. The positions of the (2J + 1)/2 Stark levels of 10 of the lowest energy multiplets were obtained. Upconversion fluorescence in the green, blue and violet while exciting the I-4(15/2) --> F-4(9/2) transition was observed and modelled via excited state absorption and energy transfer processes populating the energy levels of the S-4(3/2), H-2(9/2) and P-2(3/2) multiplets. Room temperature upconversion laser operation in the green at 550 nm has also been achieved by pumping the 1% Er3+:LiKYF5 gain medium with laser diodes at 651 and 800 nm, (C) 2001 Published by Elsevier Science B.V.